Technical Field
The present invention relates to antenna devices having a patch antenna.
Background Art
A patch antenna formed on a dielectric substrate is used for radar devices mounted on vehicles and aircraft to monitor its surrounding environment. In general, the patch antenna has a structure in which patch radiating elements (conductors having a patch-like shape) are formed on a dielectric substrate. Further, a conductive section is formed on the other surface (back surface) of the dielectric substrate which is opposite to the surface (front surface) on which the patch radiating elements are formed. The conductive section acts as a base plate. Further, there is a possible case in which the conductive section is also formed at the edge portions on the front surface of the dielectric substrate in addition to the patch radiating elements.
In the operation of the patch antenna having the structure previously described, an electric field is generated between the patch radiating elements and the conductive section, and a surface current flows due to the generated electric field on the surface of the conductive section. The surface current flows to the edge portion of the dielectric substrate. Finally, the radiation occurs from the edge portions of the dielectric substrate (i.e. the edge portions of the conductive section). This radiation becomes unnecessary radiation which affects the performance of the patch antenna. That is, the radiation from the edge portion disturbs the directivity of the patch antenna.
On the other hand, a patent document 1 discloses a technique capable of suppressing a surface current flowing on the conductive section on the substrate. Specifically, a plurality of conductive patches is formed on most of the surface around the patch radiating elements on the surface of the dielectric substrate. Each conductive patch is electrically connected to the base plate on the back surface of the dielectric substrate through a conductive via. The formation of the conductive patches makes it possible to suppress the transmission of the surface current to the edge portions of the base plate.